Human papillomavirus (HPV) is a very common virus that causes abnormal growth of tissue on the feet, hands, vocal cords, mouth and genital organs. Over 60 types of HPV have been identified and each type infects certain parts of the body. HPV is mainly spread through physical contact with an infected individual. In the majority of cases, HPV disappears within 1-2 years and indeed, during the course of the infection, may be subclinical; the individual may be unaware of their infection. However, in a small number of cases, HPV can progress and develop into cancer.
There are two kinds of abnormal tissue caused by HPV: condyloma (warts) and dysplasia (pre-cancer). Wart-like growths can be found in any infected areas and may cause itching, burning or slight bleeding. In these instances, antiviral creams may be prescribed or, in some cases, the growth may be removed or destroyed by cold cautery (freezing that destroys tissue) or hot cautery (burning warts off with an electric instrument or laser treatment).
Where HPV infection progresses to cancer, cancer patients are treated by a combination of surgery, radiotherapy and chemotherapy. However, radiotherapy and chemotherapy have the disadvantage of destroying healthy as well as malignant cells, and can thus cause severe side effects, while surgery is invasive and leaves the patient open to secondary infections. These side effects and risks are undesirable, and coupled to this is the fact that these treatments are not always successful, resulting in the majority of patients entering relapse and so representing with the disease.
It is therefore clear that more effective treatments are required, and it has been suggested that the specificity of the immune system might be harnessed against virally infected cells. This concept has been termed “immunotherapy”.
In particular, it has been shown that cancer patients have T cells that are capable of recognising their tumour cells, but these cells do not divide and differentiate into cytotoxic T lymphocytes (CTL) which are capable of killing these cells.
Cytotoxic T lymphocytes kill “target” cells, such as virally-infected cells, and have also been implicated in the “immune surveillance” of cancer cells. The majority of CTL belong to the CD8+-subset of T cells and have T-cell receptors (TCR). These TCR are able to recognise peptides when they are expressed on the surface of cells in association with class 1 major histocompatibility complex (MHC) molecules. In man, each class of MHC is represented by more than one locus; these are called human leucocyte antigen (HLA). The class 1 HLA loci are HLA-A, -B, -C, -E, -F and -G. Additionally each HLA has different alleles and Table 1 lists those alleles that have been identified to date.
When a CTL encounters an antigen/MHC complex for which its TCR is specific, it enters the cell cycle and goes through several rounds of mitosis, followed by differentiation into an effector/killer cell. Differentiation includes forming a large number of modified lysosomes that contain the cell-killing proteins perforin and granzyme. Once the CTL have killed the target cells most of them will die, although a small proportion become memory cells that can respond to the antigen quickly if it reappears.
Tumour-reactive cytotoxic T lymphocytes have been shown to mediate tumour regression in animal models (1) and in man (2), and there has thus been an interest in using tumour-specific CTL's as an immunotherapy for human cancers.
In this regard monoclonal antibodies have been shown to be effective against some cancers, especially cancers of white blood cells, and are targeted at a molecule or receptor that is associated with cancer cells. Table 2 lists some of these antibodies and their mechanism of action.
Alternatively, dendritic-cell vaccines have been used to elicit a tumour-specific CTL response. Dendritic cells are the most potent antigen-presenting cells and they act by engulfing antigen, processing it into peptides and presenting it to T cells. To make a dendritic-cell vaccine, dendritic cells are harvested, exposed in vitro to antigen associated with the type of tumour in the patient, and then re-injected into the patient. To date these vaccines have shown some promise against melanoma, prostrate cancer and lymphoma.
Ideally these vaccines target molecules that are expressed on cancer cells, but not on healthy cells. However such tumour-specific antigens have been hard to find, and as a result many of the immune agents now in use also target healthy cells in the hope that these cells, eventually, will be replaced. As with radiotherapy and chemotherapy, this treatment can cause severe side effects and also leads to the potential for autoimmunity (3). Indeed, in the case of a telomerase vaccine, this protein is also present in the stem cells of bone marrow, reproductive organs and perhaps other tissues. Further, the antigen to which some dendritic cells are exposed include tyrosinase, which is to be found in melanocytes, or prostatic acid phosphatase (PAP), which is to be found in prostate cells.
It is therefore clear that additional viral therapies are needed, particularly for those patients with an advanced stage disease that has failed to respond to conventional viral or cancer treatments.
Recently, a number of studies have shown that high-level expression of certain proteins in tumour cells is sufficient to allow CTL to discriminate between tumours and normal cells (4,5).
One way of avoiding autoimmunity in tumour immunotherapy is to target the 15% of human malignancies that are associated with viruses. Of these the strongest association is between cervical cancer and human papillomarivus, with 99.7% of cervical cancers containing HPV DNA (6). There are over 25 HPVs that infect the genital mucosa and give rise to malignancies such as cervical cancer, head and neck cancers and skin cancers. These “high risk” HPVs are characterised by at least two oncogene products: E6 and E7, which act to immortalise and transform, in the cervix, epithelial cells. The expression of these proteins is thought to be essential to retain the transformed phenotype of the cancer cell and so these non-self viral proteins are therefore attractive targets for CTL mediated immunotherapy.
CTL active against HPV E6/E7 can be induced by vaccination (7) and such CTL have been detected with variable frequency in patients with premalignant cervical disease (8) or cancer (9). However it has been difficult to generate these CTL in vitro, probably because they occur at low frequency (10). A major limitation of using these proteins as tumour-specific targets is that they are expressed at low levels in cancer cells (11). Furthermore, the E6 and E7 proteins themselves are small and contain few epitopes suitable for recognition by CTL (12).
The present invention aims to overcome these problems by identifying and then targeting peptides that are recognised by CTL, which peptides are specific to HPV transformed cells and are very unlikely to give rise to autoimmunity. These peptides are either uniquely presented or over-presented in HPV transformed cells, and the proteins from which these peptides are derived are, typically, either absent or appear to be expressed at very low levels in HPV transformed cells. In contrast, these proteins occur at normal or high levels in normal cells.
The invention is based on the mechanism that HPV E6 and E7 oncoproteins use to mediate targeted degradation of host cell proteins such as retinoblastoma proteins (Rb), C-MYC and HMCM7, among others (see Table 3), which takes place during transformation of the infected cell.
It is well known that HPV oncoproteins bind to and facilitate the degradation of host cell proteins, such as Rb. Thus, analysis of HPV transformed cervical carcinomas reveals no apparent expression of full-length Rb protein, whereas normal cells have high cellular levels of the Rb protein, as this is not normally proteolytically degraded (13).
It has been shown that Rb proteins are degraded by the ubiquitin-dependant proteolysis system (13), and more recently, it has come to light that intracellular organelles called proteasomes play a role in mediating degradation (18,19) of host cell proteins after interaction with E6 or E7 oncoproteins.
We have recognised the fact that the degradation of, for example ubiquinated protein substrates by proteasomes, is possibly the major mechanism by which peptides recognised by CTL's are generated (20, 21). For example, in a virally infected cell, newly synthesised viral proteins in the cytoplasm are degraded by proteasomes into peptide fragments. These peptides are transported into the endoplasmic reticulum (ER) by transporter associated with antigen processing (TAP) proteins. Once inside the ER, the peptides will bind to free MHC class I molecules and beta 2 microglobulin to form a mature MHC/peptide complex. This is transported to the cell surface where it may be recognised by CTL. FIG. 1 shows a diagrammatic representation of this process.
Accordingly, the present invention is based on the theory that in HPV transformed cells, Rb proteins (and other proteins, see Table 3) will be targeted for degradation, processed and peptides thereof will be presented on the surface of the cell as peptides that can be recognised by CTL. In non-HPV transformed, or normal, cells these proteins will not be degraded significantly, so these peptides, effectively, will not be available for CTL recognition. Thus, HPV transformed cells should have high levels of, for example, Rb derived peptides typically co-presented on the cell surface in a peptide HLA complex, but low intracellular levels of the full-length proteins, contrary to normal cells (FIG. 2).
The use of host cell proteins as targets for immunotherapy is not novel. However, in all previous instances this approach has relied on the over-expression of proteins in tumours, compared to normal cells. For example, host cell proteins such as p53 (5), Wilms transcription factor (WT1), Her 2/Neu (16) and hTert (17) have been proposed as “tumour-specific” antigens, as all of these are over-expressed in tumour cells. To our knowledge, this is the first time that a HPV or cancer vaccine has been directed at “tumour-specific” proteins, and more particularly peptides thereof, that are expressed at normal, low, or undetectable levels in HPV transformed cells, compared to normal cells.
Previously, high levels of antigen expression were thought advantageous in order to allow CTL to discriminate between tumour cells and normal cells.
Additionally, up until now HPV vaccines have comprised proteins that are produced by HPV, not host proteins that are targeted for degradation by this virus.
In summary, the current invention relies on a relatively high level of presentation of peptides at the cell surface but not necessarily on relatively high levels of expression, or apparent expression, of the corresponding proteins in the virally-infected cell. In fact, low level or no expression of the tumour-specific protein would typically indicate that the protein was being targeted for degradation by viral proteins and so was present at low intracellular levels, but following degradation, presented at the cell membrane and so was available as a peptide for CTL recognition.
Accordingly, in one aspect of the invention, there is therefore provided a vaccine comprising: at least one isolated, purified, synthesised or recombinant peptide, wherein the peptide is a fragment of a host cell protein that has been degraded by human papillomavirus oncoproteins, and can elicit a CTL response when administered to a mammal.
Reference herein to a cell protein that has been degraded by human papillomavirus oncoproteins includes reference to a protein that has been selectively targeted for degradation by HPV oncoproteins and so includes a protein that, in a HPV transformed cell, would be selectively targeted for degradation or a protein that is acted upon by human HPV oncoproteins in such a way that it is, directly or indirectly, degraded, most typically but not exclusively, by the ubiquitin pathway.
In a preferred embodiment of the invention the mammal is human.
Preferably, the oncoprotein is E6 or E7.
The host cell protein may be any protein that is degraded by viral proteins, such as E6 or E7, and Table 3 lists those proteins that are currently known to be targeted for degradation by E6 or E7.
Preferably, the peptide is HPV-specific or tumour-specific, meaning that it is presented in high amounts on the cell surface of HPV transformed or tumour cells, relative to normal cells.
Even more preferably, the peptide is 9 to 30 amino acids in length.
Alternatively, the peptide may be 9 to 11 amino acids in length.
The CTL response is preferably a HPV-specific or tumour-specific CTL response, meaning that the CTL can recognise HPV transformed cells or tumour cells expressing the peptides of the vaccine.
More preferably, the vaccine comprises one or more of the peptides shown in Table 4 (SEQ ID NOS: 1-161).
More preferably still, the vaccine comprises any of the aforementioned peptides plus a further protein or peptide comprising a major histocompatibility complex molecule, ideally, a class I molecule and more specifically a human leucocyte antigen (HLA), and more ideally still a HLA selected from Table 1.
In another aspect of the invention, there is provided a vaccine comprising: at least one isolated, purified, synthesised or recombinant peptide, wherein the peptide is chosen from those listed in Table 4.
In yet another aspect of the invention, there is provided a vaccine comprising: at least one isolated, purified, synthesised or recombinant peptide selected from Table 4 and, further at least one isolated, purified, synthesised or recombinant HLA selected from those listed in Table 1.
In a further aspect of the invention, there is provided a vaccine comprising: at least one isolated, purified, synthesised or recombinant nucleic acid molecule encoding any peptide or peptide/HLA complex as described above.
In this embodiment, the nucleic acid molecule may be in the form of a vector that comprises a recombinant construct. Ideally the construct is adapted for the expression of said vaccine in a selected host system. The host system is a cell, plasmid, virus, live organism or other similar vehicle.
According to a further aspect of the invention there is provided a host cell transformed or transfected with the vector of the invention.
Additionally, the present invention provides a method of manufacturing a vaccine, which method comprises; culturing a host cell transformed or transfected with a vector comprising a recombinant construct as described above; and isolating/purifying the resulting construct product.
The peptides of the present invention may also be used to generate and isolate HPV-specific or tumour-specific cytotoxic T lymphocytes or their T cell receptors or the genes encoding said receptors, in vitro, for use in adoptive immunotherapy. This could for example be carried out by culturing T lymphocytes with at least one of the peptides described above.
According to yet a further aspect of the invention there is provided a method of identifying HPV-specific or tumour-specific cytotoxic T lymphocytes comprising:    (a) culturing a sample containing cytotoxic T lymphocytes with at least one peptide that represents a fragment of a host cell protein which is degraded by HPV proteins when said host cell is transformed or transfected by HPV whereby said peptide is ultimately presented on a surface of a virally infected cell; and    (b) selecting CTL that recognise said peptide by binding thereto.
In a preferred method of the invention said peptide is one selected from the list shown in Table 4. In yet a further preferred method of the invention the CTL are CD8+ cells.
It will be apparent to those skilled in the art that CTL receptors may further be identified using the aforementioned method.
The present invention can be used to treat HPV associated diseases and particularly cancer, preferably cervical cancer, head and neck squamous cell cancer, non-melanoma skin cancers, liver cancer, mesothioloma or prostrate cancer.
Furthermore, the present invention also provides a method of treatment, which method comprises administering a vaccine as described above, to a mammal to be treated. Ideally, the mammal is human.
According to a further aspect of the invention there is provided a peptide, or a nucleic acid molecule encoding same, selected from the list shown in Table 4.
In a further embodiment of the invention, said peptide is for use as a vaccine and in particular for use as a HPV vaccine to treat HPV associated disorders.
According to a further aspect of the invention there is provided a complex comprising at least one of the peptides listed in Table 4 in association with a HLA co-presenting peptide.
More preferably the HLA peptide is one of the peptides listed in Table 1 and more specifically HLA-A binding protein and more specifically still HLA-A 0201.
According to a further aspect of the invention there is provided the use of a HPV-specific peptide for the production of a HPV vaccine wherein said peptide is a fragment of a mammalian cell protein that has been degraded by human papillomavirus oncoproteins and which is presented, in combination with HLA, at the surface of the transformed or transfected HPV cell whereby the recognition of this peptide HLA complex by a cytotoxic T lymphocyte results in the elicitation of an immune response.